ABSTRACT Genomics of Pathobionts and Transition From Colonization to Infection (Project #1) Antibiotic resistance has become a critical public health priority due to the devastating consequences that it may have on the US, world health and global economy. Among the most recalcitrant pathogens, extended spectrum ?-lactamase and carbapenemase-producing Enterobacteriaceae (ESBL-E/CRE), Clostridiodes difficile and vancomycin-resistant enterococci (VRE) are among the highest priority organisms. A common theme among these priority pathogens is that the intestine is usually the major reservoir and source of nosocomial infections. Additionally, most of what is known about clinical infectious disease pathogenesis of these organisms is based on studies that view symptomatic disease as being ?mono-microbial? in nature, considered to be dominated by the virulence mechanisms of a single pathogen alone without significant contributions from other microbes or pathogens. Moreover, a major challenge to understand the process of pathogen colonization to infection in critically ill patients is that these individuals are captured into studies at the time of event onset (i.e. when they become colonized and/or infected). This situation prevents key mechanistic insights into why only a subset of vulnerable patients develop pathogen colonization and subsequent infection and the factors that increase mortality when this process occurs. Our preliminary data show that functional interactions between these organisms are important determinants of clinical disease susceptibility and severity in vulnerable patients. Using the facilities of the Houston?s Texas Medical Center, we plan to prospectively follow two robust cohorts of highly immunocompromised and critically ill patients, namely, patients with hematological malignancies subjected to stem cell transplant (SCT) transplant and those critically ill individuals admitted to medical intensive care units (ICUs). A common feature in the care of these patients is the massive use of antimicrobials causing dysbiosis on the gastrointestinal tract. Our hypothesis, as part of this P01 application (DYNAMITE program) is that patient susceptibility to gut-derived nosocomial colonization/infection by high-threat AMR pathogens is critically dependent on pathogen adaptability (including acquisition of antibiotic resistance determinants) and host-microbiome-pathogen interactions that determine disease progression and clinical outcomes. The specific aims of this project are, i) dissect the population structure of VRE, ESBL-E/CRE and C. difficile in colonizing vs infecting isolates, ii) Identify genomic features in VRE, ESBL-E/CRE and C. difficile that correlate with major clinical outcomes and dissect the clinical impact of colonization in high-risk patients, and iii) determine the impact of antibiotic use on the dynamics of colonization/infection and development of antibiotic resistance in these gut-derived pathogens. Our comprehensive translational approach of the DYNAMITE program, incorporating genomics, metagenomics, proteomics/metabolomics and clinical features would provide novel insights into major factors that influence outcomes of critically ill and immunocompromised patients.